Depending on how you look at it, this is either the "foreigner" neighborhood or the "tourist" neighborhood (or both). You can find just about anything... and I mean ANYTHING... here. Take subway line #6 (the Brown Line) to Itaewon Station.

3 Alley Pub

One of the few proper "pubs" that I've visited in Seoul, in every respect of the word. The owner (Gunther; he's hard to miss) drinks with the patrons, the barstaff all speak English (some are even foreigners), and the beer selection is fantastic. They have a number of European beers on tap (including Hoegaarden and reasonably-priced Guinness) and even more in bottles. They have a pool table, darts, a jukebox, a few cozy booths, and a private back room. The bar is almost exclusively full of foreigners and this is a great place if you're from an English-speaking country and want to feel like you're in a bar back home.

Gecko's

Gecko's is either famous or notorious as a place where US military hang out (more so than any other bar on this list). Like the 3 Alley Pub, it has a great selection of draft and bottled beer, good pub food, and a mix of patrons. I do find that the staff are not always so friendly, though, and if you're going to see a bar fight in Itaewon, this is probably the location (I assume those two statements are related). Definitely a place to visit on your Itaewon pub crawl, though.

Hollywood Bar and Grill

It's been described to me as "Seoul's most cosmopolitan bar" and though I'm not sure I completely agree with that, there is no arguing that this fantastic bar represents a cross-roads of Western cultures. On a given Saturday night you will find Americans, Canadians, Brits, Aussies, Kiwis, and even Eastern Europeans in large numbers. The beer selection is refreshingly extensive, the bar staff are super-friendly, and the layout of the bar offers everything, regardless of whether you want a quiet booth or want to sit with "the lads" in front of English soccer and rugby on Saturday nights. The bar is open until the last customer leaves, so this is a great destination for a long night of drinking and having fun.